This invention relates to tire-changing machines and more particularly to such machines as are provided with a stand for supporting the tire to be changed in a horizontal position with upper and lower bead breakers which separate the tire bead from the wheel rim.
The prior art, as least insofar as the patent literature is concerned is voluminous. Certain patents are directed to upper bead breaker mechanisms; other patents to the lower bead breaker mechanism; and further patents to mechanisms for driving a central post and still further patents to combinations of these and other features.
The most relevant prior art known to the inventor is as follows:
______________________________________ U.S. PAT. NO. ISSUED INVENTOR ______________________________________ 3,847,198 Nov. 12, 1974 Brosen, Jr. 3,807,477 April 30, 1974 Curtis 3,742,999 July 3, 1973 Myers, Jr. 3,358,730 Dec. 19, 1967 Mandelko 3,255,800 June 14, 1966 Strang et. al. 3,212,552 Oct. 19, 1965 Foster 3,165,142 Jan. 12, 1965 Tabordon 3,158,190 Nov. 24, 1965 Foster 3,064,718 Nov. 24, 1962 Brosene, Jr. ______________________________________
Elements of these structures have been and are still employed in commercially available machines, for example the double lower bead breaker shoe, of U.S. Pat. No. 3,158,190, the pneumatically powered machine with the single lever co-action between the upper and lower bead breakers and the central drive post of U.S. Pat. No. 3,212,552; the hook-shaped upper bead breaker of U.S. Pat. No. 3,255,800; and the various mechanisms of U.S. Pat. No. 3,847,198; U.S. Pat. No. 3,807,477 and U.S. Pat. No. 3,742,999.
However, the development of alternative wheel rims such as magnesium or alloy wheels together with the wider ranges of sizes of wheel rims has made the use of these machines increasingly difficult and has resulted in unsatisfactory performance.
For example the standard wheel structure usually employs a flange on the wheel rim of between 3/8" and 1/2" as compared to the wider flange of 3/4" on alloy wheels. With many conventional tire changers of either the single or double lower bead breaker type the locus followed by the leading edge of the lower bead breaker shoe is usually an arc of a circle. While the wheel-receiving table top may accommodate different sizes of wheel rims such a path does not permit accommodation of wheel-rim flanges of differing width. Thus while such a lower bead breaker may effectively break a bead on a standard wheel rim it will frequently hit the wheel rim with either the first or second lower bead breaker shoe. Since the tire obscures the view of the operator considerable damage can be done to the alloy or magnesium wheels. The operator may not detect the wrong engagement and the rim may be fractured or dented.
A similar problem arises with upper bead breakers of the prior art. These may take the form shown in U.S. Pat. No. 3,255,800 to Strang previously referred to, or they may have the form shown in U.S. Pat. No. 3,807,477. The two types referred to are entirely different in structure and action and give different difficulties.
With the second type the column which supports the upper bead breaker is pivoted to move about a single pivot point and again the bead breaker arm moves through an arc. In this type of structure the "nose" of the bead breaker arm engages the bead or the sidewall of the tire. The arcuate motion of the bead breaker tends to pull the bead breaker nose outwards and downwards and the engagement between the bead breaker "nose" and the side wall is not too secure. This frequently results in the "nose" sliding off or a downward and outward pull being exerted on the wall. This action is not always effective in breaking the tire bead at the rim.
In the first mentioned structure a nose is provided to engage the inner surface of the wheel rim. The rotational pull on the bead-breaker column is translated into an outward horizontal force against the wheel rim and a downward force against the tire sidewall or bead. The horizontal force may be as great as 25,000 lbs. This force frequently damages the wheel rims particularly if they are of alloy.
The "nose" of this first-mentioned upper bead breaker is also provided with a secondary arm which is spring-loaded to maintain it in engagement with the tire bead and follow the tire bead into the wheel well. However, the mechanism does not so function in practice throughout the travel of the bead breaker column. Frequently, after the upper bead breaker column has completed part of the travel the bead will not break because the vertical force is not sufficient to break the bead. The operator then drops the upper bead breaker column relative to the turning lever and repeats the bead-breaking procedure so that the bead can be broken. The upper breaker mechanism which has just been discussed also has a further difficulty in that the adjustments available to the operator are limited by the provision of limited pivot points at the bottom of the vertical column and relatively fixed relationship of the bead breaker shoe to the "nose" which is itself pivoted at one point. No meaningful lateral adjustment is available without changing the force exerted on the bead to break it.
Machines of the prior art have three further principal shortcomings, their complexity and cost; and a further operational problem. The second of these arises because the centre post driving mechanisms usually drive through a limited range and since they usually rely on a simple hydraulic power source are provided with a spring return to reverse the motion. However, in operation when the operator inserts the tire tool in the bead and over the centre post and rotates the tire tool to pry the bead from off the wheel rim, because the bead is normally broken in the bead-breaking operation over a limited range, the tire tool frequently binds between an unbroken section of rim and bead. The result is that the tool is stuck and the spring return does not provide sufficient power to release the tire tool so that another attempt can be made.
With these difficulties in mind it is the object of the present invention to provide an improved tire-changing machine which is economical to build, easy to operate and which may be operated with a minimum of damage to wheel rims.
In accordance with the present invention there is provided in a tire-changing machine for breaking tire beads on a wheel rim having a drop centre an improved bead breaker mechanism which comprises: power means, a bead breaking shoe having a leading edge engageable with a tire bead; bead breaking shoe support means connected to said power means; and guide means for guiding said leading edge of said bead breaking shoe through a locus inward toward said tire bead and said wheel rim drop centre.
In accordance with another aspect of the present invention there is provided in a tire changing machine a frame mounting a wheel rim in a generally horizontal position, an upper bead breaker support column mounted generally vertically in said frame, an upper bead breaker shoe, means for mounting said shoe to said support column so that said shoe extends generally laterally therefrom said mounting means comprising a column lock member having an upper wall and a lower wall spaced from said upper wall, said walls each having a thickness significantly less than the spacing therebetween, said walls having aligned apertures which are slightly larger than a cross section of said support column for receiving said column therethrough, whereby force applied to the shoe having a force component parallel to the longitudinal axis of said column urges opposite edges of said aligned apertures to assume high pressure contact with adjacent surfaces on said column providing frictional resistance to movement of said means for mounting along said column.
Further in accordance with the present invention there is also provided in a tire-changing machine power means, an upper bead breaking mechanism, a lower bead breaking mechanism, lever means connected between said power means and said bead breaking mechanism for actuating said bead breaking means in response to actuation of said power means; and drive means operably connected with lever means for rotatably driving said centre post in a first direction and a second reverse direction about a vertical axis.
There is also provided in a tire-changing machine having a frame, a platform for receiving a wheel rim having a drop centre mounted on top of said frame, and a rotatable shaft having a free upper end extending from said table, the improvement which comprises a pair of reversely coacting fluid motors each with pistons, the piston of a first fluid motor being operatively connected with a first bead breaker shoe and the piston of a second fluid motor being operatively connected to a second bead breaker shoe; one of said pistons being further operatively connected to said rotatable shaft to drive said shaft in first and second reverse directions about a vertical axis, and individual guide means for guiding the travel of each of said bead breaker shoes in a locus inward toward said wheel rim drop centre.